Waves Flashcards
What is a progressive (moving) wave?
Something that carries energy from one place to another without transferring any matter
What is the frequency of a wave?
1/period
What is the wave equation that links the wave speed to the frequency and wavelength?
Wave Speed = Frequency x Wavelength
How to use an oscilloscope to find the speed of sound?
Use a signal generator to generate a frequency of 2-6khz
Adjust the dials on the oscilloscope until there is at least one complete cycle
Change the distance between the mic and the speaker so that the peaks of one wave
line up with the troughs of the other wave.
Measure the distance between the mic and the speaker
Calculate the frequency of the wave by measuring the period
Move the mic until the wave on the oscilloscope moves 1 wavelength and the troughs line up again.
The difference between the two distances is the wavelength
Repeat this process and find a mean wavelength and then calculate the wave speed using the formula
What are transverse waves?
e.g electromagnetic waves
The vibrations (oscillations) are perpendicular to the direction of the wave
What are longitudinal waves?
e.g sound waves
The direction of the vibrations(oscillations) is parallel to direction of the waves is travelling
What does it mean for a wave to be reflected?
When a wave hits a boundary and bounces back
What does it mean for a wave to be refracted?
The wave changes direction as it enters a different medium, due to it speeding up or slowing down.
What is intensity?
A measure of how much energy a wave is carrying.
I= P/A
What are the properties of EM waves?
They travel at 3x10^8 in a vacuum
They are all transverse
They can all be polarised (like all transverse waves)
Like all other progressive waves, they can carry energy
What does it mean to polarise a wave?
Forcing a wave to oscillate only in a single plane of direction. It can only happen in transverse waves
What is the relationship between polarization and reflection?
When light reflects it is partially polarised
What effect does reflection have on the intensity of light?
At certain angles, light is partially polarised, causing a change in it’s intensity
How can you use polarization to cause the intensity of a wave to be 0?
When there are two sources of polarization that are perpendicular to each other, the intensity is 0
What is an interface?
The boundary between 2 different meida
What happens to ultrasound waves when they hit an interface?
They are partially reflected and partially transmitted through the media
What are ultrasound waves?
Waves that carry a frequency beyond the 20khz human hearing range
What are ultrasound scans?
Short pulses of ultrasound radiation from images inside the body
What process is used for ultrasound scans?
Ultrasound is directed into the body using a transducer
A gel is used to remove air pockets between air and skin and increase the penetrative effect on the ultrasound
When the ultrasound meets the interface inside your body (between different types of tissue) some of the ultrasound is reflected
A computer times how long it takes for the wave to return and uses that information to calculate the distance
Using the information it’s calculated the computer can generate an image
How can you produce a clearer image from an ultrasound?
By having shorter pulses ( but not so short that they interfere with the transmission of the transducer)
Shorter wavelengths as they diffract less
What is superposition?
When two or more waves pass through each other
What is the principle of superposition?
When two or more waves pass over each other the resultant displacement is equal to the vector sum of the individual displacements
What is constructive interference?
When two displacements (crest and a crest) or (trough and trough) superpose and add together to give a bigger displacement
What is destructive interference?
When two or more displacements add together and cancel each other out.
